Deviations from Bimaximal Neutrino Mixing

Neutrino mixing is described by one small (possibly zero) and two large (one possibly maximal) angles. This makes the bimaximal mixing scenario a valid zeroth order scheme. Since however solar neutrino mixing is non-maximal by close to 6σ, deviations from this scheme have to be considered. First we give a useful parameterization of these deviations. Using that the PMNS matrix is given by U = U lep^dag U_ν , where U_lep stems from diagonalizing the charged lepton mass matrix and U_ν, diagonalizes the neutrino mass matrix, we discuss deviations stemming from charged lepton mixing when the matrix U_ν is assumed to be of bimaximal form. We generalize the procedure to a priori non-maximal atmospheric neutrino mixing in U_ν as predicted by the flavor symmetry L_e - L_μ - L_τ.